Fetch repositories with remote ID if possible (#1078)

Use IDs of the forge to fetch repositories instead of their names and owner names. This improves handling of renamed and transferred repos.

TODO

- [ ] try to support as many forges as possible
    - [x] Gogs (no API)
    - [ ] Bitbucket Server
    - [x] Coding (no API?)
- [x] update repo every time it is fetched or received from the forge
- [x] if repo remote IDs are not available, use owner / name to get it
- [x] handle redirections (redirect a renamed repo to its new path)
- [x] ~~pull all repos once during migration to update ID (?)~~ issue fixed by on-demand loading of remote IDs
- [x] handle redirections in web UI
- [ ] improve handling of hooks after a repo was renamed (currently it checks for a redirection to the repo)
- [x] tests
- [x] `UNIQUE` constraint for remote IDs after migration shouldn't work (all repos have an empty string as remote ID)

close #854
close #648 partial
close https://codeberg.org/Codeberg-CI/feedback/issues/46

Possible follow-up PRs
- apply the same scheme on everything fetched from the remote (currently only users)

Co-authored-by: 6543 <6543@obermui.de>

server/remote/coding/coding_test.go

@@ -108,7 +108,7 @@ func Test_coding(t *testing.T) {
 
 		g.Describe("When requesting a repository", func() {
 			g.It("Should return the details", func() {
-				repo, err := c.Repo(ctx, fakeUser, fakeRepo.Owner, fakeRepo.Name)
+				repo, err := c.Repo(ctx, fakeUser, "", fakeRepo.Owner, fakeRepo.Name)
 				g.Assert(err).IsNil()
 				g.Assert(repo.FullName).Equal(fakeRepo.FullName)
 				g.Assert(repo.Avatar).Equal(s.URL + fakeRepo.Avatar)
@@ -119,7 +119,7 @@ func Test_coding(t *testing.T) {
 				g.Assert(repo.IsSCMPrivate).Equal(fakeRepo.IsSCMPrivate)
 			})
 			g.It("Should handle not found errors", func() {
-				_, err := c.Repo(ctx, fakeUser, fakeRepoNotFound.Owner, fakeRepoNotFound.Name)
+				_, err := c.Repo(ctx, fakeUser, "", fakeRepoNotFound.Owner, fakeRepoNotFound.Name)
 				g.Assert(err).IsNotNil()
 			})
 		})